The following patents and patent publications, and patents that issued from these publications, are incorporated in their entireties by reference: CA2639732 (A1), U.S. Pat. No. 7,582,365, U.S. Pat. No. 7,267,889, U.S. Pat. No. 7,763,573, U.S. Pat. No. 6,887,530, U.S. Pat. No. 7,179,507, U.S. Pat. No. 7,008,462, U.S. Pat. No. 7,135,240, U.S. Pat. No. 7,052,527, U.S. Pat. No. 6,808,756, U.S. Pat. No. 5,976,695, U.S. Pat. No. 5,434,210, U.S. Pat. No. 5,196,471, U.S. Pat. No. 5,506,055, U.S. Pat. No. 5,122,182 and U.S. Pat. No. 5,049,450.
OEM manufacturer spray powders that form abradable coatings to improve turbine engine efficiency. These abradable powders are generally sprayed onto a surface using plasma or low velocity combustion processes. It is known that in many plasma applications for clearance control coatings, also known as abradable coatings, these coatings are sprayed using: 1) blends of polymer and metal or ceramic or 2) blends of solid lubricant and metal or ceramic or 3) co-sprayed with polymer or solid lubricant and ceramic or metal.
One form of powder for thermal spraying is composite powder such as disclosed in U.S. Pat. No. 3,617,358 (Dittrich). This patent teaches the use of the spray drying process for making the composites, involving the spraying of a slurry of very fine powdered constituents with a binder to form droplets, and drying the droplets into a powder. There may be only a single constituent, or multiple constituents may be incorporated, for example in a cermet powder of a metal and a non-metal.
Other composite forms are known for thermal spraying, for example metal cladding of a ceramic core as disclosed in U.S. Pat. No. 4,291,089 (Adamovic). According to this patent a clad powder such as nickel alloy clad bentonite is useful for producing thermal sprayed abradable seal coatings for gas turbine engines. Cladding of metal core particles with finer particles of ceramic is taught in U.S. Pat. No. 3,655,425 (Longo and Patel) for similar purpose.
Another example of a powder for thermal spray is disclosed in U.S. Pat. No. 5,122,182 (Dorfman). This patent discloses a two constituent blend, however both constituents are a metal plus a non-metal, and they are approximately the same, with certain predetermined ratios. Thus, it is also known that the prior art teaches a 3 phase (matrix (metal or ceramic))+solid lubricant+polyester abradable material.
Although the prior art coatings meet the design intent of applications, there are reliability and high cost issues with the previous powders and processes used to make the coatings. Accordingly, what is needed is an improved powder for use in forming abradable coatings.